An interesting post on Mixtures & cheminformatics on designing a new file format to handle mixtures of chemicals, in particular things like "LDA within a solvent mixture of THF and hexanes, in a ratio of 1 to 7".
The format hasn’t been locked down yet, but it is very simple: it’s JSON-based, in order to make it easy to read & write with any software platform, and have high human readability. It’s hierarchical, making it possible to describe mixtures-of-mixtures, which happens frequently. Each component is expected to provide a structure and quantity whenever these are known, with name being also highly encouraged. Other information like canonical identifiers, database links, cross references, etc., can easily be encapsulated – the Mixfile is intended to be an inclusive container of information – but they do not necessarily impart much-if-any special meaning to the software that interprets them.
More info can be found on the GitHub page https://github.com/cdd/mixtures.